Expanding-type fastening device for detachable interconnection of hollow structural details

ABSTRACT

An expanding-type fastening device for detachable interconnection of hollow structural details comprises an expansible core made of rigid material, such as metal, and a coating of elastic material, such as plastic, fixedly arranged on the core.

United States Patent [191 Offenbroich Aug. 21, 1973 [54] EXPANDING-TYPE FASTENING DEVICE 3,094,338 6/1963 Page 279/1 Q UX FOR DETACHABLE INTERCONNECTION Z133: 0F HOLLOW STRUCTURAL DETAILS 3:645:569 2/1972 Reilly 287/54 A Inventor: Adrian Gottfried Offenbroich, Sodra Forstadsgaten 49, 211 43 Malmo, Sweden Filed: Nov. 9, 1971 Appl. No.: 197,056

Foreign Application Priority Data Nov. 10, 1970 Sweden 15146/70 References Cited UNITED STATES PATENTS l/l934 Bellerive 306/34 FOREIGN PATENTS OR APPLICATIONS 548,983 7/1956 Belgium 287/2 Primary ExaminerMervin Stein Assistant Examiner-David H. Corbin Attorney-Francis C. Browne et al.

[5 7] ABSTRACT An expanding-type fastening device for detachable interconnection of hollow structural details comprises an expansible core made of rigid material, such as metal, and a coating of elastic material, such as plastic, fixedly arranged on the core.

Town, gnawin 'n'giies mum atwted Aug. 21, 1973 3,753,583

FIG. I PRIOR ART EXPANDING-TYPE FASTENING DEVICE FOR DETACHABLE INTERCONNECTION OF HOLLOW STRUCTURAL DETAILS This invention relates to an expanding-type fastening device for detachable interconnection of hollow structural details, and said device comprises expanding members which are adapted to nest in each of the structural details and which can be expanded by means of at least one expanding member operable from outside.

A plurality of such expanding-type fastening devices are known already. They all suffer from various drawbacks whether they are made of metal or plastic, which are the two most common types of material utilized. Plastic, however, does not provide a sufficient stability in complex constructions. On the other hand, the use of metal entails many advantages, which is proven by the fact that the current expanding-type fastening devices are mostly made of metal. Nevertheless, metallic material is disadvantageous from other aspects, which will appear from the following embodiment which is cited by way of example.

A prior art expanding fastening device of the type outlined in the foregoing is intended for detachable interconnection of pipes or tubes of quadrangular cross section, for which reason the expanding members are likewise of quadrangular cross section, diagonally slotted and have expanding elements in the form of cooperating screws which are accessible through apertures in the tubes which are preferably of aluminium. Arranged between the expanding members is a non-slit intermediary member in the shape of a cube which re mains visible after the device has been mounted. The device is made in an integral piece of metal, preferably an aluminium alloy.

Although the expanding-type fastening device described must be considered very satisfactory in point of function and has met with great commercial success, it is associated with certain drawbacks.

Thus, it is not entirely satisfactory in point of function that once the device has been expanded contact is established between two metal surfaces of relatively low friction. To attain a satisfactory engagement the expanding member will have to be heavily expanded. On the other hand, if the expanding member is not entirely smooth the irregularities thereof will become visible on the outer side of the tube. Besides, point contact may arise between the two cooperating parts with resulting poor engagement. Finally, the material of the expanding member does not revert to initial position once expansion has ceased. It has even happened that, because of the material properties, expanding members have ruptured in use.

The construction outlined in the foregoing suffers from drawbacks also in point of manufacture. For the reasons given, a rather exact machining of the expanding members is required, and this is true to a still higher extent for the intermediary member interconnecting the expanding members, as said intermediary member must have a pleasing finish. Because of these and other drawbacks that are associated with the manufacture the prior art expanding-type fastening device described by way of example is relatively expensive.

The above disadvantages are eliminated by the present invention which is characterised in that the device in combination consists of a core which is made of a rigid material, such as metal, and the expanding member elements of which are slotted, and a coating of elastic material, such as plastic, fixedly arranged thereon.

This combination of materials is advantageous from several aspects in point of both function and manufacture.

At the manufacture the surfaces of the device need not be very thoroughly machined and the core may advantageously consist of several simple metal details which need not even be mechanically interconnected but can be held together with the aid of the plastic coating subsequently applied, which coating is of optional thickness within certain limits. The device is then ready for use without further machining. This considerably reduces the cost of manufacture, and the appearance of the device will be equally pleasing or even more pleasing than before and has a much more resistant surface than the earlier finely machined and often painted metal surface. The fastening device according to the present invention is considerably cheaper in manufacture than the previously known devices, which is a very important and decisive factor.

However, more important from a functional aspect is that the elastic coating will provide a distribution of forces between the expanding member and the tube throughout the engagement surface and also a better nesting engagement of the parts with smaller expansion forces owing to the increased friction; the engagement can be further improved by arrangement of minor projections at the inner side of the tube. Any risk of visible markings on the outer side of the tube is eliminated. Another important functional advantage is that the elastic coating tends to return the expanding member to the initial position after finished expansion. It should also be mentioned that the otherwise dirt-collecting diagonal slot in the expanding members can be fully covered by the coating, which in most cases is caused to cover all of the surfaces of the core.

The invention will be more fully described hereinbelow with reference to the accompanying drawing in which:

FIG. 1 is a perspective view of a prior art expandingtype fastening device;

FIG. 2 is a side view of an expanding-type fastening device according to the present invention; and

FIG. 3 is a section on line III-III in FIG. 2.

FIG. 1 by way of comparison shows a prior art fastening device I intended for detachable interconnection of pipes or tubes 2 of quadrangular cross section. This device incorporates diagonally slotted expanding members 3 and an interconnecting non-slotted intermediary member 4 in the form of a cube. The expanding members can be expanded with the aid of cooperating screws 5 which are accessible through apertures 6 in the tubes 2.

This device suffers from all of the drawbacks outlined in the foregoing.

In order that the advantages mentioned in the intro duction shall be attained in this particular case (viz. detachable interconnection of tubes of quadrangular section and expansion of the expanding members with the aid of cooperating screws) a core consisting of simple welded iron parts can be provided (as shown in FIGS. 2 and 3) with a coating of an elastic material, such as polypropylene or nylon.

The fastening device shown in FIGS. 2 and 3 thus comprises a core 7 the horizontal portion of which (see FIG. 2) is formed by two parallel adjoining iron rods of semi-circular section and the vertical portion of which likewise is formed of semi-circular iron rods 7a, 7b which are welded at 8 to the two first iron rods so that these will also be welded together. As will appear from FIG. 3 the resulting dividing cut between the iron rods will be diagonally located in relation to a tube 2' of quadrangular section, which is indicated by dash-anddot lines.

The core 7 thus formed is provided by a simple onestep plastic casting operation with an elastic coating 8 which is fixedly arranged thereon and preferably completely covers the core and which also constitutes the cube 4' separating the expanding members. The expanding members of the expanding device can be given a square cross sectional shape by reason of the coating, but it is more suitable to cut off the corners as shown in FIG. 3 in order to provide room for the contemplated expansion of the elastic coating material and in order that the layer covering the dividing cut shall not be too thick to prevent spreading each expanding memher.

In this case also, expansion of the expanding member is effected with the aid of screws which cooperate with one another at the dividing cut.

it is heavily stressed that the embodiment of the fastening device illustrated in FIGS. 2 and 3 should be considered merely as an example of the invention and that several modifications are conceivable within the scope of the appended claim. Thus, of course, the principle of the invention can be exploited in fastening devices for detachable interconnection of structural details formed with holes of any cross sectional shape whatever, and the device need not be expanded with the aid of cooperating screws. Moreover, the parts forming the core need not be interconnected as the coating can keep the parts together to the extent required, and the cube-shaped intermediary member 4' illustrated may be dispensed with in many cases. Finally, the parts forming the core may be simple bent sheet metal details or a cast body, for example of the appearance illustrated in FIG. 1.

What I claim and desire to secure by Letters Patent 1. an expanding-type fastening device for detachably interconnecting tubular structural elements, said fastening device comprising an elongated core member formed from a rigid material such as metal and adapted to be telescopingly received in one of said structural elements, a longitudinally extending slot formed in and dividing said core member into segments along at least a substantial portion of the length thereof, at least one expansion member engaging said core and operable from outside the tubular structure element for moving said segments relative to one another to expand said core, and an elongated sleeve of elastic material such as plastic fixedly mounted on and substantially covering the outer peripheral surface of said core and bridging said slot, whereby upon operation of said expansion member to move said segments to an expanded position spaced from one another within a tubular structural element said coating will be expanded into tight frictional contact within the inner surface of the tubular structural element, said sleeve being dimensioned to apply a radially compressive force to said core tending to move said segments toward one another from their expanded position upon operation of said expanding means to permit movement of said segments toward one another.

Il k i k 

1. AN EXPANDING-TYPE FASTENING DEVICE FOR DETACHABLY INTERCONNECTING TUBULAR STRUCTURAL ELEMENTS, SAID FASTENING DEVICE COMPRISING AN ELONGATED CORE MEMBER FORMED FROM A RIGID MATERIAL SUCH AS METAL AND ADAPTED TO BE TELESCOPINGLY RECEIVED IN ONE OF SAID STRUCTURAL ELEMENTS, A LONGITUDINALLY EXTENDING SLOT FORMED IN AND DIVIDING SAID CORE MEMBER INTO SEGMENTS ALONG AT LEAST A SUBSTANTIAL PORTION OF THE LENGTH THEREOF, AT LEAST ONE EXPANSION MEMBER ENGAGING SAID CORE AND OPERABLE FROM OUTSIDE THE TUBULAR STRUCTURE ELEMENT FOR MOVING SAID SEGMENTS RELATIVE TO ONE ANOTHER TO EXPAND SAID CORE, AND AN ELONGATED SLEEVE OF ELASTIC MATERIAL SUCH AS PLASTIC FIXEDLY MOUNTED ON AND SUBSTANTIALLY COVERING THE OUTER PERIPHERAL SURFACE OF SAID CORE AND BRIDGING SAID SLOT, WHEREBY UPON OPERATION OF SAID EXPANSION MEMBER TO MOVE SAID SEGMENTS TO AN EXPANDED POSITION SPACED FROM ONE ANOTHER WITHIN A TUBULAR STRUCTURAL ELEMENT SAID COATING WILL BE EXPANDED INTO TIGHT FRICTIONAL CONTACT WITHIN THE INNER SURFACE OF THE TUBULAR STRUCTURAL ELEMENT, SAID SLEEVE BEING DIMENSIONED TO APPLY A RADIALLY COMPRESSIVE FORCE TO SAID CORE TENDING TO MOVE SAID SEGMENTS TOWARD ONE ANOTHER FROM THEIR EXPANDED POSITION UPON OPERATION OF SAID EXPANDING MEANS TO PERMIT MOVEMENT OF SAID SEGMENTS TOWARD ONE ANOTHER. 